In recent years, a solvent-soluble fluoroolefin copolymer containing hydroxyl group or carboxyl group has been used as an ultra-high weather resistive coating resin, and the use thereof has been increasing. It is known that copolymers of fluoroolefin with vinyl ether, vinyl ester or the like, which are proposed in, for example, JP-B-60-21686, JP-A-3-121107, JP-A-4-279612 and JP-A-4-28707, are soluble in usual solvent for paints, and in combination use with a curing agent such as isocyanate or melamine, can be baked or cured at normal temperature to form coating films excellent in weather resistance.
However, those coating films have a problem that, when the films are exposed outdoors, stains in the air and in the rain water are easy to adhere to and deposit on a surface of the coating film (problem in stain-proofing property for preventing adherence of stains). In order to improve wipe-off property of carbon stains and marking ink (stain removable property), reaction products of fluoroolefin copolymer and silane compound were investigated in, for example, JP-A-4-173881. Also in U.S. Pat. No. 3,429,845 and JP-A-4-275379, there are proposed compositions of hydroxyl group-containing fluoroolefin copolymers and a hydrolysis product prepared by adding water and a catalyst (hydrochloric acid, etc.) to a silicate (monomer) or a silicate condensate (oligomer) and then hydrolyzing the mixture in alcohol. However, those compositions cannot offer the effect of improving the above-mentioned stain-proofing property.
Examples of employing a silane compound as a curing moiety as mentioned above are also proposed in JP-B-45-11309, JP-A-5-78612, JP-A-61-258852, JP-A-62-116673, JP-A-64-75575, JP-A-2-232221, JP-A-2-240153, JP-A-4-211482, JP-A-4-65476 and JP-A-4-292677. However, curing is insufficient due to large contents of alcohol and water. On the other hand, since a silicate originally has hydroxyl group or requires high temperature baking, migration of the silicate to the surface of coating film is inhibited. Also there is a problem that since the silane compound has a non-hydrolyzable group, hydrophilic property is insufficient. Due to the mentioned reasons, the stain-proofing property is not improved like the above-mentioned other proposals.
The situation is the same with respect to other paints of acryl, acrylic silicon, inorganic materials or the like, and a coating film having remarkably improved stain-proofing property is scarcely known. The present situation is such that though silane compounds are used as a dehydrating agent at the time of polymerizing or dispersing pigments, almost all amount of the silane compound reacts with water during production process and thus, the effect of improving the stain-proofing property of the resulting coating film is scarcely obtained.
Further as disclosed in, for example, W094/06870, W095/02645, JP-A-7-48540, JP-A-7-102211, JP-A-7-136584, JP-A-7-173429, JP-A-7-82520, JP-A-7-109435 and JP-A-7-60184, techniques using organometallic compounds for improving stain-proofing property have been proposed, but those techniques cannot satisfy requirements with respect to hydrophilic property of a coating film surface, repeatability thereof, stain-proofing property, curability, compatibility, recoatability, storage stability, pot life, floating resistance, antifoaming property, workability in coating and cracking of the coating film surface.
An object of the present invention is to provide a composition for paints being capable of forming a coating film which is remarkably excellent in stain-proofing property whereby neither stains in the air nor stains marked due to rain water adhere to or are deposited on the coating film surface, and to provide a stain-proofing agent for adding to the composition.